Recently, there has been increasing interest in micromachined acoustic transducers based on the following advantages: size miniaturization with extremely small weight, potentially low cost due to the batch processing, possibility of integrating transducers and circuits on a single chip, lack of transducer “ringing” due to small diaphragm mass. Especially, these advantages make the micromachined acoustic transducers, such as microphone and micro speaker, attractive in the applications for personal communication systems, multimedia systems, hearing aids and so on.
Micromachined acoustic transducers are provided with a thin diaphragm and several diaphragm materials that must be compatible with high temperature semiconductor process, such as silicon nitride and silicon have been utilized as diaphragm. However, micromachined acoustic transducers made by these conventional diaphragm materials suffer from a relatively low sensitivity and it is mainly because of the high stiffness and residual stress of these diaphragm materials.
In order to implement the micromachined acoustic transducers with competitive performance with conventional acoustic transducers, it is necessary to find new diaphragm materials that have low stiffness and compatibility with semiconductor processing at the same time. Also, the transducer should be designed to release or minimize the residual stress of the diaphragm.